I have a 350 and 150 in my garage, but water could easily be drained and filled through a nearby window or door as well, for tanks in the house. I have a 65 gallon, wheeled rubbish container. I have a pump and heater inside of it. I fill it, add dechlorinator and let it run for at least eight hours to warm. I siphon waste water out of the tank and just let it run down the driveway. I then pump water out of the rubbish container into the tank to refill it. If I need more than 65 gallons, I refill it with the garden hose and then add hot water from inside the house to bring it up to the correct temp. When not in use, I store the container outside. I have used this system for several years and it has worked well.